Thermodynamic control of diameter-modulated aluminosilicate nanotubes

The diameter of imogolite nanotubes was regulated by altering the synthesis temperature and was characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and ²⁹Si cross-polarization magic angle spinning nuclear magnetic resonance (CP-MAS NMR). Imogolite diameter modulation via thermodynamic control was induced by curvature formation of the proto-imogolite cluster, which was dependent on the degree of silanol (SiOH) substitution. At lower temperature, 323 K, the amount of SiOH substitution in the proto-imogolite clusters decreases and accordingly reduces the hydrogen bonding among SiOH substituents. In contrast, at higher temperature, 371 K, the large amount of SiOH substitution in the proto-imogolite clusters increases the hydrogen bonding among silanol groups, which also increases the degree of the curvature. The proto-imogolite clusters with a larger curvature can quickly create tubular structures by forming a circle with a smaller diameter.